1. Field of the Invention
The present invention relates to a radiographic image capturing apparatus and a radiographic image capturing method for irradiating an object to be examined of a subject with radiation emitted from a radiation source while an irradiated field of the radiation on a radiation detector is being delimited by a collimator, and converting the radiation that has passed through the object to be examined into a radiographic image with the radiation detector.
2. Description of the Related Art
There have heretofore been developed biopsy apparatus for sampling a tissue of a biopsy region (e.g., a lesion region in a subject's breast) in an object to be examined of a subject and thoroughly examining the sampled tissue for a disease diagnosis. In order to sample the tissue reliably, the biopsy region needs to have its three-dimensional position specified in advance.
It has been customary to carry out a stereographic image capturing process on a radiographic image capturing apparatus by irradiating the object to be examined with radiation from a radiation source disposed at two different angular positions and detecting the radiation that has passed through the object to be examined with a radiation detector to acquire two radiographic images of the object to be examined, and calculate a three-dimensional position of the biopsy region based on the acquired two radiographic images.
The irradiated field of the radiation on the radiation detector is delimited in advance by a collimator which is disposed between the radiation source and the radiation detector, or more specifically the object to be examined that is positioned on the side of the radiation detector which faces the radiation source (see Japanese Utility Model Publication No. 54-032458 and Japanese Laid-Open Patent Publication No. 08-107891).
As described above, the three-dimensional position of the biopsy region needs to be specified in advance in order to sample the tissue of the biopsy region reliably. Therefore, if the radiation is applied to at least the biopsy region in the stereographic image capturing process, then it is possible to calculate the three-dimensional position of the biopsy region based on the two radiographic images which include the biopsy region.
However, the radiographic image capturing apparatus according to the related art has the irradiated field of the radiation fixed in all stereographic image capturing processes. In other words, the collimator does not adjust the irradiated field before and after each of the stereographic image capturing processes. During the stereographic image capturing processes, therefore, the radiation is also applied to body regions of the subject which have nothing to do with the calculation of the three-dimensional position of the biopsy region, and hence the subject is unduly exposed to the radiation.
In the stereographic image capturing process, the biopsy region may not be included in the two radiographic images or either one of the two radiographic images due to a movement or positional or angular change of the object to be examined between stereographic image capturing processes or due to angular errors of the radiation source at the two angular positions. If the biopsy region is included in only one or neither of the two radiographic images, then the three-dimensional position of the biopsy region cannot be calculated accurately. As a result, the tissue of the biopsy region cannot properly be sampled by the biopsy apparatus.